1. Field of the Invention
The present invention relates to an electroconductive polymer solution, an electroconductive polymer composition, and a solid electrolytic capacitor therewith and a method for producing the same.
2. Description of the Related Art
Solid electrolytic capacitors, which are obtained by forming a dielectric oxide film on a porous body of a valve metal such as tantalum or aluminum by anodic oxidation method and thereafter by forming an electroconductive polymer on this oxide film to be a solid electrolyte, are developed.
These solid electrolytic capacitors have an equivalent series resistance (hereinafter, referred to as ESR) lower than that of a capacitor in which the solid electrolyte is manganese dioxide conventionally used, and they are used for various purposes. Recently, solid electrolytic capacitors having a low ESR, a large capacity, and a small loss are required with a trend of high frequency and high current of an integrated circuit.
The methods for forming an electroconductive polymer layer that comes to be a solid electrolyte of this solid electrolytic capacitor are roughly classified into chemical oxidative polymerization and electrolytic oxidative polymerization. As the monomer constituting an electroconductive polymer material, pyrrole, thiophene, 3,4-ethylenedioxythiophene, aniline and the like are known. Also, recently, there is a method in which an electroconductive polymer solution is applied to form a solid electrolyte.
The electroconductive polymer solution is generally provided as a dispersion or a solution in an aqueous solvent or as a solution in an organic solvent, and the solvent is removed at the time of use to be used as an electroconductive polymer material. It is variously studied as antistatic materials, electromagnetic shield materials, electrodes of capacitors, electrochemical capacitors and the like, electrodes of dye-sensitization solar cells, organic thin film solar cells and the like, and electrodes of electroluminescence displays. Recently, in order to provide an electroconductive polymer material having a higher performance, the developments regarding a method for producing an electroconductive polymer solution and regarding a composition, for example, in which an additive is added to provide a new function, is actively carried out.
As a technology regarding the electroconductive polymer solution, technologies, in which the hydrogen ion index (pH) of the electroconductive polymer solution is arbitrarily adjusted when the electrode is produced in consideration of the inherent acid resistance of the electrode and the jointing material, are disclosed as follows.
JP 2006-249128 A relates to a technology to provide an electroconductive polymer solution and an electroconductive paint film in which the corrosion of the metal and the discoloration of the contact material can be prevented, and discloses a technology regarding an electroconductive polymer solution which contains a 7-conjugated electroconductive polymer, a polyanion and a solvent and in which the pH is adjusted to 5 to 13.
JP 2006-287182 A relates to a technology to provide a capacitor and a method for producing the same in which the corrosion of the dielectric layer is prevented, and discloses a technology regarding a capacitor in which the solid electrolyte of the capacitor contains a π-conjugated electroconductive polymer, a polyanion and a solvent and which is formed by applying an electroconductive polymer solution in which the pH is adjusted to 3 to 13.
JP 2011-82314 A relates to a technology to provide a solid electrolytic capacitor in which the high capacity and the low ESR are maintained as well as in which the heat resistance is high, and discloses a technology regarding a solution for a solid electrolytic capacitor which contains at least water and/or water and a mixed solvent, an electroconductive complex of a cationized electroconductive polymer and a polymer anion, and a hydroxy compound with a melting point of 170° C. or higher, in which the hydrogen ion index of the solution is adjusted to a range of pH 3 to 13.
As for the method for adjusting the pH of the electroconductive polymer solutions of JP 2006-249128 A, JP 2006-287182 A and JP 2011-82314 A, a method by mixing an alkali, an amine, an imidazole, a pyridine or the like in the solution of the complex of the 7-conjugated electroconductive polymer and the polyanion to form a salt, a method by esterifying the acid group, a method by amidating the acid group or the like is carried out.
WO 2007/091656 relates to a technology to provide a capacitor in which the electroconductivity of the solid electrolyte layer is excellent, the ESR is low, and the heat resistance and the voltage resistance are also high, and discloses a technology regarding a capacitor in which the solid electrolyte of the capacitor contains a π-conjugated electroconductive polymer, a polyanion and an amide compound, and which is produced by applying an electroconductive polymer containing a π-conjugated electroconductive polymer, a polyanion, an amide compound and a solvent to a solid electrolyte.
However, although the pH of the electroconductive polymer solution can arbitrarily be adjusted by these methods, on the other hand, the property and the heat resistance of the electroconductive polymer film is not always sufficient in the electroconductive polymer composition obtained from this electroconductive polymer solution, resulting that there remains a problem.
The present invention has been realized to solve the above-mentioned problem. The object thereof is to provide an electroconductive polymer solution in which the good dispersibility of the electroconductive polymer solution is maintained and the pH is arbitrarily adjusted, to provide an electroconductive polymer composition having an excellent heat resistance, and also to provide a solid electrolytic capacitor having an excellent reliability and a method for producing the same.